High-frequency apparatus



I Sept. 27, 1949. s A: E. HARRISON 2,482,769

u HIGH-FREQUNCY APPARATUS Filed Dec. 28, 1344 s sheets-sheet 1 UUTPI/ T HMPL/ Tl/DE ORNEY Sept. Z7, i949.

A. E. HARRISON HIGH-FREQUENCY APPARATUS 5 Sheets-Sheet 2 INVENTOR Aww/UR EJ/ARR/sa/v ATTORNEY Filed Dec.

Sept. 27, 1949.

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A. E. HARRISON HIGH-FREQUENCY APPARATUS 5 Sheets-Sheet 3 vINVENTOR BY ,Kg/mm;

ATTORNEY v Patented Sept. 27, 1949 UNITED STATES PATENT OFFICE HIGH-FREQUENCY APPARATUS Arthur Harrison, Rockville Centre, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application December 28, 1944, Serial No. 570,134

13 Claims.

l The present invention is directed to ultra high yfrequency apparatus, especially of the cavity resknown, as illustrated by Fig. 2 of U. S. Patent No. Y '2,250,511.

In such devices an electron beam is projected through a cavity resonator to be velocity modulated thereby, and is thereafter reflected and returned into theV resonator in a grouped condition to sustain oscillations in the resonator. Such devices therefore operate on the velocity modulation principle as oscillation generators.

In the present invention, no reliance is placed on Velocity modulation, but a new principle, which may be termed transit-time modulation, is used instead. By the term transit-timemodulation is meant the periodic variation of :the transit time of the electrons of the stream between two points, at a predetermined transittime-modulating frequency, whereby these eleclation may be utilized in accordance with the.

principles of the present invention.

By the use of this novel principle of transittime modulation, the present invention permits utilization of devices of the reflex type for the first time -as frequency multipliers or amplifiers. This is possible by operation inY an entirely different manner, not relying on velocity modulation as in the prior devices. According to the vpresent invention, an electron stream is reflected into a cavity resonator or other high frequency energy-extracting device. The transit time of the stream is varied at a predetermined frequency, which produces electron grouping of the Vstream as it 'enters the resonator. These grouped electrons may deliverenergy to the resonator at the predetermined frequency, producing amplifier action, or at a frequency harmonically related to the predetermined frequency, producing frequency multiplication. f

As a feature ofthe invention, the transit-time Cil For this purpose the elecmodulation is produced by superposing afield of the predetermined frequency upon the retarding or reflecting field needed to reverse the flight of the electrons of the stream.

Accordingly, it is an object of the present invention to provide improved methods for and structure of electron discharge devices and apparatus operating on the principle of transit-time modulation.

It is a further object of the present invention to provide improved electron discharge apparatus of the reex type and circuits and methods therefor useful in performing frequency multiplication, amplification, modulation, etc.

It is a still further object of the present invention to provide improved reeX electron discharge devices and circuits and methods for producing frequency multiplication or amplification by transit-time modulation.

A further object of the invention is to provide improved apparatus and methods embodying novel features and kprinciples adapted for use in realizing the above objects and also inA other fields.

0 The invention in another of its aspects relates to novel features of the apparatus described herein for achieving the above and other objects of the invention and to novel principles and 'methods employed inthis apparatus, as used according to the above-mentioned objects or in other elds.

Further objects and advantages will be apparent from the following specification and drawings, wherein o Fig. 1 is a schematic circuit diagram of one Fig. 5 is a schematic circuit diagram of a modified form of the present invention;

Fig. 6 is a schematic circuit diagram of an improved electron discharge device and circuit therefor operating according .to the present iny vention; Y

Fig. 7 is a schematic circuit diagram of an improved electron discharge device operating according to Vthe present invention and adapted Aboth to oscillate and to multiply frequency;

Fig. 8 is a schematic diagram of a modified thereof;

Fig. 11 is a schematic circuit diagram ofa modification of the apparatus of Fig. 9 and including a self -oscillating frequency 'multiplier'circuit; t

Fig. 12 is a schematic diagram `of a modified form of electron discharge device useful with`the circuit of Figs. 9 or 11; t K

Fig. 13 is a schematic circuit diagram oistill another form of the present invention adapted for use at higher powers:

Fig. 14 is a schematic diagram of a further form of electron discharge device useful in practicing the present invention; and

"Figi l5 is a schematic diagram of an improved electron discharge device embodying the principle ofthe present-invention and adapted for` amplication or modulation.

Referring to'Fig. 1,`there is shown schematically at' I I "an lelectronL discharge' device Vofthe type disclosed in Fig. 2 of Patent No. 2,250,511 which "has been termed acreflexvelocity-modulated elec- Y tron' discharge device. This'device II includes a 'conducting cavity or hollow resonator I2 usually maintained at static ground potential and having a pair of electron-permeable grids or electrodes I3, I4'forming a narrow gap between their sup-wl Vable accelerating battery I5 havingits negative '-"terminal connectedto'cathodel andthe positive terminal connected through ground-tof the "resonator I 2 and the entrance'.grid'lll thereof.

On rthe opposite side of grids I3\,I4 fromcathode I5 isA a' reflector electrode II which, in the prior l art, is usually maintained at a constant potential Urslightly negative` or Vpositive ormequal to that of c the cathode I5.

With* proper relation lamong (a) the accelerating voltage between cathode'l and grid Ill. (b) the resonant frequency of resonatorfl 2, and (c) the potential applied to reflector electrode Il, ultra high frequency 4oscillations,

. substantially equal in frequency to the resonant frequency of resonator I2, may begenerated in resonator I2, which oscillation might be supplied to' any suitable output or load circuit by means of an output terminal "I8, usually in the form of a coaxial transmissionl liney terminating in a coupling loop within resonator I2.

In the prior art it has been customary to'maintain the reflector voltage constant when using the device as an oscillation generator, since it is 'found that variationin this voltage changes the output frequency. When desired, `the output could 4be modulated by superposing a modulating signal on the reflector voltage.Y However, the range of useful' amplitudes of modulating signal is limited by the inherent characteristics-of the 'l device, as will lbeapparent from'Figl 2.

` Fig. 2"'illustrates a graphwhose independent v`rvariable or abscissa isthe reflector-to-ground voltage V land whose dependent yvariablel or ordinate is the-output 'amplitudefor energy supplied 23 to a load by terminal I8. The graph of Fig. 2 is plotted for a fixed resonator frequency and a xed accelerating voltage supplied by battery I6. The curves A, B and C of Fig. 2 then represent the output amplitude of the reflex oscillator of the prior art as the reflector voltage is varied.

It will be seen that output is derived only for `ffcertain ranges -of reflector r'voltagefsuch as V1 to V2. V3, to V4, V5 to Vs, etc. In each of these re- .gions maximum output is obtained only for a "predetermined particular voltage or voltages dififp'eriodic'ally in-V velocity.

"electrode I'I retards these electrons.

` feringonly slightly therefrom.

According to the accepted theory of operation `of*.suchi'devicesjthe electron stream is velocity 15"' "timeswithinithisf-retardingv field, those? 'of'ihigher ":velocity approaching reflectorl I'I more 'closely land hence lhavingflonger paths than. thoselfof "-l'lower: velocity which are reflectedmore `'quickly f" and whichA have shorter paths.

As a `result V"ofthe velocity modulation, i electrons @passing through grids I II, I 3"'at` differing 'instants' '-of time-will 'return to exit grid I3 substantially simultaneously if inv the form 'of a"bunchforgroup fof electrons.

"When such a bunch or group 'of electronsarrives 1 back at'gridV I3 at the instant at' which the elec- -fztri'c-eld between-"grids 14,2 I3 'is of a polarity op- AV Yposing or retarding 'the flow V-of these velectrons "fand of maXimumf/amplitude, maXimum'renergy 'will' be delivered from- .theA electrons-t.' theeld,

r and'oscillationsfofthe resonant frequency ofiresonator 'I2 will be sustained therein.

fl By fch'anging.' the reflector voltage; the raver- *age-transit ltime of the Aelectrons Vin the-retarding 0" eldl is `correspondingly varied. By 'this :adjust- `ment,`the electrongroups -can be-madeto return to grid1 |3`after reflection in'. any desired-phase l -relative` tof 4the' resonator field. f However, vany substantial .variation inreflector voltage will materially-alter this given phase relation, `and will #materially-decrease the amplitudefof oscillation,

orl may stop voscillationsentirelyas when the ad- "justed lreflector' voltage isv between V2 'and V3, for example. vAccordingly, if a modulating'voltage-is applied to `the reectorzelectroda Vthe 'output may vbe 'vared. Y`I-Iowever,` if the modulating voltage is'of` too-great "amplitude, the reflector 'voltage may'beswung so far as toprevent oscillations completely For this reason, the range of variation 'of the'modulating voltage had to bev kept relatively small inthe prior'art.

vfvThe above :discussion of thev prior` art reflex Voscillator is necessaryA to understand 'the principles of the present invention which, as will be shown, is not an oscillator but is a'frequencymul- According to the present invention, when used as a frequency multiplier, the potential of re- -ilector I1 is no vlonger kept constantybutis varied periodically at the frequency to be multiplied,

electrode I'I may thus'have its potential varied at the fundamental frequency. In this case re- "llector electrode "II is connected to the tuned ,-fsecondary I9fofI a transformer 2I to whose primary 22 is fed the fundamentalfr'equency'wave l-to which-secondary u"I9 Vis tuned. The'iother'terminal of secondaryY I 9 is connected to the negative terminal of a suitable source of reflector voltage indicated schematically by battery 23, whose positive terminal is grounded. vBatteries 23 and I E may be formed by the same power supply and are preferably each adjustable as indicated.

By thus varying the reflector electrode at the fundamental frequency f, the electron stream is caused to be grouped at this frequency f. However, this grouping is not sinusoidal but contains a large percentage of harmonicfrequency content. Accordingly, the retraverse of the grids I3, I4 by this fundamentally grouped stream Will excite resonator I2 at the harmonic frequency to which this resonator is tuned, thus producing frequency multiplication. Y

The following is believed to 4be a true explanationof the principles of operation of Ithe present invention.

' Asa rst approximation, let it be assumed that the electron stream passing exit gridY I3 has uniform velocity; that is, all the successive electrons have the same velocity. Referring to Fig. 3,`curve D represents the variation of instantaneous reflector voltage V as a function of time, just several cycles of this reiiector voltage of frequency f being indicated. Va is the average or unidirectional component of the negative reiiector voltage with respect to ground, and VM is. the amplitude of the alternating component of fr mdamental frequency (D f-a VM is therefore one-half the total swing in reiiector voltage. The instantaneous refiector voltage canvthen be'expressed as V=VR+VM cos wt. The equation of motion of the electrons will then be given by %=-ab cos wt n Where :c is the distance fromv the exit grid I3 measured toward the reflector I'I, a is a constant proportional to h s y j where s is the exit-grid-to-reiiector spacing. and `b is a constant proportional to The constant a determines the l average transit time of the electrons in the retarding field, and b determines the degree of bunching. y i,

By integration, this equation of motion becomes where t1 is the instant of Vtime the electron under consideration enters the reflecting field through grid I3, and F1(t1) and F2(t1) are functions of t1 given by 'Uu being the uniform and assumed 'constant entering velocity of the electron. 1 7

In Fig'. 3 there is also plotted, against the same time scale, the paths of electrons entering the refleeting field atspaced intervals of the period T of the fundamental frequency voltage. These curves are plotted'with assumed values of a and b `giving approximately two fundamental frequency periods as the average round-trip transit time. This value is illustrative only, since transit times as low asV of the order of 1/2 cycle, or muc larger than 2 cycles, may be used.

As shown in Fig. 3, electron No. II enters the reflecting field when it is most negative and is reversed'quickly about one cycle later when the eld is again most negative. Electron 3 enters the reiiecting field when it has average value; thusthis electron experiences a less negative retarding field during the first part of its travel and accordingly proceeds farther toward the re-l flector electrode. Also, it is not reversed so quickly, because the field is not so negative for it. Therefore it has a. longer transit time than electron Il. Electron -B enteringV the retarding field at its maximum positive value has'l man average retarding field during its initial travel and has about average transit time. Electron 9 entering the retarding field at its average value has a more negative retarding field during its initial travel, and has a short transit time. The in-between electrons behave similarly. In general, electrons 4 through 8 arrive almost instantaneously at the exit grid I3 after traversing the retarding field space, and are accordingly hunched ElectronfB forms the Center of the bunch, the electrons leaving grid I3 just lbefore it l ltaking longer transitztime, and those leaving grid I3 just after electron `6 taking less transit time, so that all thesejelectrons arrive back at grid I3 almost together, as a bunch. 'Y

Since the bunching which thus takes placeis solely due to difference in transit times, with0ut any Vof the prior art velocity modulation, the electrons ,leaving grid I3 may be said to be transit-time modulated by thefundamental rfrequency voltage on reflector I 1.

A The solid-line curve of Fig. 4 shows the return time t2 of the electrons at grid I3 after reflecting, as a Yfunction of the timetr they entered the reflecting field through grid I3. This figure shows howl electrons 4 through 8 arrive almost together at about the same time t2.

Fig. 4 also indicates generally the wave form of the electroncurrent returning -to grid I3, since the slope of the'curveisthe reciprocal of the electron current density. Where the slope is zero, asy near positions 5 and '7, the current density is theoreticallyini'lnite, giving two infinite peaks of ,current density per fundamental cycle. This non-sinusoidal Wave form for the current shows that it is rich in harmonics, sorthat, by tun-ing resonator I2 to a harmonic frequency, it will be excited to oscillate at that harmonic frequency. In practice, frequency multiplication ratios of 11 to 1 and 19 to 1 have been attained with ease.

An important advantage of the present invention is that, by making the average reflector voltage VR negative with respect to the cathode, no current flows to the reflector, and substantially zero fundamental frequency drive power is required. In this Way, the drive equipment is made relatively simple and inexpensive.

The aboveanalysis was made on the assumption that the entering velocity of all electrons was constant (vo). Actually, since these electrns pass through resonator I2 before entering tlie reflecting space, they will be velocity modu-` lated :and fW-ilL therefore have periodically .varying velocities. However, the effect of this velocity modulation A-is slight and has little or no ultimate effect; on the operation. The dotted curve of Fig. 4-shows lhow-the situation is` modified ina 3 to l multiplier, The third harmonic velocity modulation merely produces more innite current density peaks, and, if anything-enriches the harmonic content of -thevbeam, thereby improving operation. f

The present invention can operate in two somewhatrdiffering modes, either as a stabilized .or lock-in oscillator, or asan actual driven .frequency multiplier. In the first mode, as alock-in oscilla-tor, the average reflector voltage VR is adjusted so that it falls-within one of the regions A,l,B,-C,;shown in liig.` 2, so that oscillations will be produced by ordinary reflex action. at a. frequencyi near to the desired frequency; this near frequency may be termed the free-running frequency. The application of a fundamental frequency voltage of even relatively small amplitude to the reflector electrode .then so varies the condition of oscillation of. resonator I2 as to prevent stable oscillations except at the exact harmonic ofthe fundamental frequency, adjacent to the free-running frequency. The stronger the. fundamental voltage, the stronger is the lock-.in tendency. If the fundamental frequency is cutoff, the oscillatorwill continue to oscillate at the near-by .free-running frequency.

Inlthe. secondmode of operation, any arbitrary average reflector voltage may be used, evenrone betweenV'z and V3, for example, in Fig. 2. The fundamental frequency voltage then produces the bunching described above, purely by transit-time modulation, andlharmonic .frequency output is derived onlyso long as the fundamental frequency isv applied. This is truefrequency multiplication. action.

As discussed. above, the average transit time of the electrons inthe reflecting-field space is determined by the averagepotential VR of the reector electrode. This potential is not critical, since optimum bunching for frequency multiplication can be obtained -for a Wide range of VR by adjusting the fundamental frequency voltage amplitude VM. However, While adjusting Va over a range of values producing a change in average transit time of one period of the fundamental n frequency voltage, it is found that -for apart of this range ofv values a negative resistance effect occurs inthe reflector field space; that is, there is a tendency for oscillations `to be set upin this space by transfer of energy from the electron stream.` For. another portion of this range, a loadingeffect occurs; thatv is, there is an ab.- sorption ofy energy Aby thefelectronstream. The latter effect is undesirable, since it increases the power which the fundamental frequency source must'fsupply. The negative resistance effect .is advantageous, since it reduces the input power requirements. Under some circumstances, Vthe input source could be dispensed with entirely,

the fundamental frequency oscillations being set other circuit diagram .of a modification .of the invention, more adapted for use at highfunda: mental frequencies. This device differs from Fig. l Imerely, in the manner in which the fundamental frequency voltage is appliedv to reflector electrode- I'I.v In this instance, a parallel transmission line formedby conductors 26 and .21 is short-circuitedat one end high-frequency-wise by `an adjustable short-circuiting device 28con ductively-connected to conductor 26 at` point 29 and capacitively coupled `to conductor.21.at.3|. The other endof .conductor 23 is connected .to reflector electrode I'Lvvhile the other end of con,- ductorff'l is connected to resonator I2, which grounded. `Ihelunidirectional component of .the reflector voltage is derived from a variable tap 32 onbattery I6 and is connected to reflector I1 through a suitable radio frequency choke Acoil .33 which prevents reflector electrode I'! from being grounded in a highfrequency sense throughbattery I3.' ConductorsziV Vand 21 and the shortcircuiting device ES'forms a short-circuited twowire transmission line, which at resonance, as is known, is equivalent to a parallel resonant cir,-- cuit.A The resonant frequency of this circuit 'may be adjusted by adjusting the short-circuiting device 2 8 along the line, preferably `to resonance at the fundamental frequency, Y

Inductively coupled to 'the line 25-21 is .a single-turn loop of wire 34 which is connected tothe source of fundamental frequency energy through any suitable highv frequency conductor, illustrated as a twisted pair 36, but which may be in the form of a further two-wire transmission line or coaxial line. The operation of the device of Fig. r5in frequency multiplication is the same as that of Fig. 1. 4

Fig. shows a further embodiment ofthe invention havinga greatlyimproved fundamental frequency input circuit and especially adapted for use with still higher fundamental frequencies approaching the ultra high' frequency or microwave range. In this instance, the reflector electrode I1- is capacitively coupled toa tubular conductor-4I by means of a cylindrical extension 42 connected lconductively to and supporting reflector I1. Tubular member 4I forms the reentrant pole of a reentrant resonator 43 which is selected or adjusted to be resonant at the fundamental frequency. In order to reduce the physical 'size of resonator 43 iforlower fundamental frequencies of this range, a conductive plate or flange 44 is carried by'or formed as an integral extension of reflector electrode I1 parallel to the Wall of resonator I2 carrying the exit grid I3.' This flange 44, in cooperation with grid I3 and its supporting wall, provides capacity loading for resonator v43, permitting reduced size for the given fundamental frequency. Reflector electrode Il is insulated in a direct current sense from resonator-4t. Whichis grounded'by direct conductive contact with resonator I2. If desired, an .insulating spacer may be inserted between extension 42 and member 4I.. The eXtensionAZ of reflector I'I is then connected to the negative terminal of adjustable reflector potential source 23 to supply the unidirectional component or average value ofthe reflector voltage. Fundamental frequency energy may .be supplied to resonator 43 by any suitable input terminal such as 46. In this -way resonator 43 :is excited at the fundamental frequency and produces an alternating electric 4field component betweenfreflector I1 and exit grid I3 .of this fundamental frequency, superposed upon the constant. reflecting eld. Accordingly, the device of Fig. 6 will operate in exactly the same manner a's the previous modifications described. The device of Fig. 6 is especially advantageous when operating with the negative resistance characteristic discussed above. With the -proper adjustment of the average reflector voltage provided by source 23, or the accelerating voltage provided by source I6 (or both), the fundamental frequency input supplied to line 46 may be omitted. Then fundamental frequency oscillations will be set up within resonator 43, which will produce transit-time modulation, and will also produce llitrmonic frequency energy in output resonator Fig. 7 shows a further embodiment of the invention in which the source of fundamental frequency energy is built. into the frequency multiplierl of the present invention. For this purpose reflector electrode |1 serves as the anode of a .conventional vacuum tube section located within the same envelope as the reflex device Thus, adjacent to reflector |1 on the side thereof opposite the resonator |2 is a control lgrid 5| having a second cathode 52 on its opposite side. Cathode I 52, control grid and electrode |1 serve as a l conventional'triode device. It will be understood that the present form of the invention is not restricted to a triode, but any type of known electron tube may Vbe thus formed, such as pentodes, hexodes, heptodes, etc.

An oscillator circuit is connected to electrode |1, control grid 5|, and cathode 52 in such manner as to cause electrode |1 to vary in potential with respect to the grounded exit grid I3 at the fundamental frequency. Fig. '7 illustrates a simple Hartley oscillator thus connected. In this figure, a tunable tank circuit is formed by adjustable condenser 53 and inductance 54. One terminal 56 of this tank circuit is connected directly to electrode I1. The other terminal 51 is connected to control grid 5| through a blocking condenser 58. A tap 59 of the inductance 54 is connected through an anode potential source 6| to the cathode 52, the'negative terminal of source 6| being connected to cathode 52. In this way by proper tuning of the circuit 53, 54 and adjustment of tap 59, as is well known, oscillations of the fundamental frequency will be set up in this tank circuit and will cause the potentia1 of electrode |1 to vary at this frequency with respect to point 51, which is connected in alternating current fashion to ground and grid I3 through by-pass condenser 62. also connected the reflector electrode potential source 23, having its positive terminal grounded and its negative terminal connected to point 51. In this way the average potentia1 of electrode |1 will be provided by the voltage across battery 23, and the alternating fundamental frequency voltage across the tank circuit 53, 54 provides the alternating component of the reflector voltage. The remainder of the apparatus of Fig. '1 then operates in exactly the same manner as discussed above to produce frequency multiplication, since the potentia1 of reflector electrode |1 is caused to vary at the fundamental frequency.

Fig. 8 shows a modification of the device of Fig. '1, in which supplementary cathode 52', control grid 5| and anode I1 are formed concentrically as cylindrical. electrodes. The end face of cylindrical anode |1' serves as reflector |1. The device of Fig. 8 may be connected to an external .circuit in the same manner as in Fig. 7.

Between point 51 and ground is Iny the abovedescribed embodiments of the the conventional reex velocity modulation electron discharge devices whichvhave come to be known bythe trade-name Reflex Klystron. Figs. 6 to 8 illustrate special forms of electron discharge device, particularly usefulin the present novel frequencyv multiplier apparatus. In allof these forms, however, some slight velocitymodulation at the harmonic frequency will be encountered, since the electron stream ltraverses the output harmonic resonator twice. As discussed above relative to Fig. 4, such velocity modulation has relatively small effect, but may be useful where a lock-in type of frequency multiplier is desired Iwhich may operate in a freerunning condition when the funda-mental frequency input is cut off. However, such velocity modulation may, under some circumstances, be considered undesirable, and is not an essential part of the present invention in its broader aspects.

Figs 9 and 10 illustrate a form of the invention which eliminates this velocity modulation and relies solely upon the transit-time modulation principle discussed above. In this Ymodification of the invention a specially Vformed resonator 66 is utilized, having an annular gap61 surrounding a central ,axial opening 65. Gap 61 is defined by an annular grid 68 adjacent to an annular collecting surface `69 .formed in the wall of the resonator. Located within the central opening 65 is a suitable electron-.emissive cathode 1|, illustrated as of the indirectly heated thermionic type. An accelerating grid 12 is positioned across the-opening65 and is connected to the resonator casing, which is grounded at 13. Grid 12 may be independent of resonator 66, if desired. Cathode 1I is maintained at a negative potential with respect to grid 12 by means of battery 14 having its negative terminal connected to cathode 1| and its positive terminal connected to grid 12 through ground. In this way cathode `1| and grid 12 form an electron gun which produces a uniform velocity cylindrical electron stream. Any otherysuitable form of electron gun may be utilized in place of these electrodes. Y

Located in the path of this electron stream is a reflector electrode 16, to which is applied a potential negative with respect to grid 12 and differing slightly from that of the cathode 1|. This potential is applied by means ofan adjustable volta-ge source 11 connected between cathode 1| Vand reflector electrode lli.y The reflector electrode 16 is specially formed to reverse the flight of the incident cylindrical electron beam and to return these electrons in the form of an annular electron stream. For this purpose reflector 161s formed with a central reentrant tip 18 which spreads the cylindrical electron stream incident thereon and converts it into the desired annular form. The reversed annular stream is then projected through annular grid 68 across gap 61, and is then collected by the collecting surface 69. If desired, the collecting surface 69 may also -be formed as an electron-permeable grid, in which case a suitable electron collector will be disposed in the path of the stream beyond this grid. This latter arrangement may be desirable Where secondary electrons formed by the electron stream impinging on surface 69 might be undesirable or harmful.

Also impressed on reflector electrode 16 is an alternating potential of fundamental frequency v f derived from a source schematically indicated 11 vvat l9.and connected-'between'the'ireflector 'I6 VVand cathode 1I. -Any Asuitable connect-ion -of `sourcelilfto reflector^16^rnay-be used. vInthis way, inhaccor'dance vvithv the principles discussed above;- the uniform-velocity electron stream passing-throughgrid`-12 is transit-time-modulated ati-the fundamental frequency'ef and isreturned ltl'irough the gap 61 of resonator'. 66inal hunched condition,r whereby it #delivers -ultrahi'gh freqi-1ency1energ-y` ofthe harmonic frequencytofthis resonator L66. 'This\ harmonic frequency.- energy hmay then beV suitably extracted vby an output-ter- =1fmina1"10for use as desired.

ItrWill be` `seen ythat 'the4 apparatus of Figs.` 9

and 1lflzoperates .purely .onthe transit-time modu- -lation principla since novelocity modulation foc` ".cursiin'the :sense util-izedin the prior artdevices, theielectron .streamt-entering. the reflecting. field A5.spacefbeing.ofuniform velocity.

Fgillshows -ea modicationofthe .deviceof i `r:tran'sit-time :modulation: principle .of the. lpresent 4invention "ifllheoscillator tankcircuit is formed by'inductcancel 83;y .anduvariable .capacitance 84 connected 1in paralleltherewith. .Oneterminal of this tank ..rcirouit.=83,: 84:.fis..directly :grounded at .86. The ..iotherzterminalzof.theftankncircuit 84 is con- ..;nected to 4grid: 82 througha-direct current blocking..rcondenser8.1. Cathode 1l is connected to an :intermediateadjustable tapl of coil 83.1through .n.a'furthersblocking condenserLBS.

zzGroundedanodeelectrode'12 :is connected to the :positive terminal..ofanelectron-accelerating ...voltagasourcel by virtue of. itsground connec- E:itionnflll .f Cathode' 1l. is-'maintainedata negative potential swith' respect to.` anode Y l2 I'by i-ts con- -1 inection to han@ adjustablei -tap 92 of .zbattery 9 l through a radio frequency choke coil-1193. Con- .i-trolagridnZw-is:suitably biased with-respect to s cathode 'H' by'fits connectionwtovalfurther varia- :ble teni-94 of source ISMV -through-.another radio frequency chokecoil 1.96. "In this v-Waycathode -l l control-grid. 82 andA `anode L l2.` are connected `.in asconventionalsoscillator circuit .land-produce oscillations in. the'- tank circuit`83,^1v84 of the :..fundamentalV frequency f.

LA ffsutable voltage- -ofthis fundamental fire- .rquency-]..is:1theny derived from anladjusta-ble tap 2.984 on `c0ilf83'andapplied lto ther reilectonelec- Iztrode 516 through'a-blockingcondenser 91; The average unidirectional potential offreflector- 16 i-isffderived Vfrom-a 1further-adjustablef tapI 99v of batteryifll .through a lradio'i'requency choke coil ill .-.Which.\preventsshort-circuitingy of reilector #electrode I6-to ground-Withr respect to' high fre- -L-quencies.

- i AIn= athis way the electron stream f emitted `-f-rom Y' cathode'f'l lfrst functions -to create fundamental "frequency oscillations. l'lhereater it enters the reflecting-'held spaceand -istransitie-time moduflated to multiply this fundamental 'frequency and produce harmonic frequencyenergyin theharmonic resonator 56 in--ithe lmanner discussed uabove. This `i-frequencyemultiplying action is assistedto'some 'extentby Lthefact that the elecxtronefstrea-rn4v` entering the" reflecting fieldV space through grid l2 tis varied in-current-intensity fat" the: fundamental frequency lcyavirtueV of-the -tentiala-the phase/of this current Yvariation-'at 'fundamental frequency can `be adjustedto cooperatetwith. the transit-time `modulation-at the .fundamental Vfrequency to enhance the harmonic energy output=froml=the device. Thefoptimum :condition is obtained when the electrons yform- .iing the centerof the bunch produced by transitvtime-modulation are most .-nurnerous, ande-the electrons between the bunches are least numerous;..that is, the'bunch electrons should `pass-grid v82 when it is nearliits maximum potential-land ismostpositive.

:Fig l2 illustrates a slightly diffe-rent type Iof .electron-discharge fdevice useful -in/-either ofthe .circuits ofFigB orr 1l.

,electrode FES is planar, .while the cathodestruc- In. Figi l2 the reflector turell'. is arrangedito haveits ernissivesurface vinrthe formA oftawvery shallovvI cone,` instead 4of 1 .beingnlataasLinthe prior gures. PThe=reson gator-16S is .identicaliwith.that of. Figs. 9v andA l1. :The modified. form of. catl'iode-v'li` and reflector Tit ..produces...the same. type of .electron ilow` as in. thefppriorliigs. 9.and 1l, so thatthe device ofFig.. v12..Will .operate .in exactly the same `manner as these figures. A..controlgrid..82,also

.of` shallow -conical conliguration isinterposed l.between cathode 1| .and anodey grid'lZ, vas in Fig. ll.

.igr 131 shows 4a further vform.v of electron- -discharge device adapted 'for performing 1 the V4same functions .as' the .prlorenibodiments of the invention. .In this instance, al1-annular cathode |32 .;is; disposed. ina slightly; dished .connguif-an tion and has- .adjacent to vit .an accelerating electronrpermeable ,.gridflike ...anode m3 .which is preferably .maintained .at ground potential.

-..C.a,thode -iil2;may be .heated by any suitable heater..meanseindicatedischematically at; EGA. A

Ybattery 'E65 y'.maintains ...anode-grid v |83 highly ...dotted lines This converging stream is reected ilected cylindrical Astreamwas indicatedby Ythe 568. This reflected ystream then ...enters `a .resonatorlll .by way-of an entrance by a variable biasingsource H2. of 'the reflector electrode IQ? isalsovariedat .the

.-.gridll disposedopposite .to yan anode Il! and f .providing va .narrow gap .therebetween in which .theelectriceld ofthe'resonator .lis concentrated.

The.average.potential ofthe reflector electrode ll relative to the .cathode yIinay. be adjusted The .potential fundamental frequency f by the source4 leconnected therewith gin any suitable manner. Resonatorg'lS is then'tuned to a desired harmonic of this fundamental frequency, and harmonic frequencyfenergy maybeextractedby. its out- -put couplingA H3 as in the preceding arrange- J-alolecoo'lingineans v.irld'lrnay `be providedfor pro- Hviding ciroulatingmoolant `to the `.outer .faceof the collecting A anode il vI l .sfere extracting. -.;there from the heat generated by electronsimpinging thereon. If desired, electrode 1 1 1 `could be made permeable to the electrons, in which case a separate collector'anode would be provided. It will be understood that a control grid might be interposed between cathode 162 and 4accelerating' electrode or anode 103. This-control grid may be suitably biased as desired, or may be connected in self-oscillating circuits as in'fthe preceding figures. Y Y

Other forms of electron discharge device suitable for use in the present invention Will be evident. For example, it is not necessary to `con-A vert yfrom a cylindrical stream to an annular stream by reflection as in Figs. 9 through 12, or to convert from an annular stream to a cylindrical stream as in Fig. 13. If desired, the electron gun may produce a cylindrical stream of electrons which, on reflection, retains its cylindrical formV on enteringl the resonator, as

shown in Fig. 14, wherein the electron gun 121` produces a cylindrical stream of electrons of constant velocity which is reflected by the planar reflector electrode 122 and then projected through the gap |23 of resonator 124 similar to resonator 1119 of Fig. 13. The device of Fig. 14 illustrates a resonator gap and electron collector arrangement which may also be used inV Fig. 13. Again, in Fig. 14, by varying the Voltage of reflector 122 at Vthe fundamental frequency, harmonic frequency energy to which resonator 124 is tuned may be extracted therefrom by its output line 126.

In each of the above arrangements the resonator may be made adjustably tunable and, when provided with a wide enough tuning range, may be tuned to several different harmonics of the fundamental frequency. In this way the same device may selectively produce energy of different harmonic frequencies of the fundamental frequency and may be used, for example, as the local oscillator in a multi-channel system havinga fixed frequency separation between channels.

equal to the fundamental frequency.

In each of the above-described embodiments' of the present invention transit-time modulation has been utilized for the production of frequency multiplication. However, the present invention contemplates a broader use for such transit-time modulation, and Fig. .15 illustrates an amplifier device operable in accordance with the principles of transit-time modulation. The device of this gure is provided with an output cavity resonator 131 which is substantially identical with the resonator of Fig.'9, 11 or 12, havinga central accelerating electrode 132, an annular Yresonator gap |33 defined by annular grid |34, and an electronintercepting or collecting surface |36, which may be replaced by a second annular grid, if desired. In such case, a separate electron collector is provided. Reflector electrode |31 has its lower surface shaped similar to reflector 16 .to convert the cylindrical electron beam passing through `grid'132 into a reflected annular beam passing acrossthe resonator gap 133.

Electrode 131 cooperates with grids 132 and 134 to form the gap of the input resonator 138, at which gap the concentrated electric field of the resonator 138 appears. For this purpose reflector 131 is formed in the end of a cylindrical member 139 capacitively coupled at 141 to the grounded wall of resonator |38. Reflector electrode 131 is maintained at a suitable average potential negative with respect to ground by itsconnection to a source indicated rschematically at 114l 142k1V Similarly, cathode |35, located opposite the grounded accelerating grid 132, is maintained at a suitable negative potential with respect to ground by a source 143. The average potential of reflector electrode |31 may be slightly negative Y orpositive with respect to that of cathode |35,

and is preferably adjustable foroptimum opera-y tion.

The high frequency wave to be amplified is supplied tothe input reesonator 138 by an input coupling 144. In this way the resonator |38 is excited to oscillation at the input frequency, toV

which it is substantially tuned, and an alternating high frequency field .of this input frequency appears between reflector 131 and grids |32 and |34. This alternating field is superposed on the negative unidirectionalretarding field provided by source 142 connected to reflector |31. The constant-velocity electron stream projected into the resonator 138 through grid 132 is `therefore reflected and transit-time modulated by this field in resonator |38. The electron stream therefore becomes grouped or bunched and is therefore capable of yielding high frequency energy of the input frequency to the field of output resonator 131 at the gap 133, the output resonator 131 being also substantially tuned to the input frequency. This output energy will be amplified with respect to the input and may beextracted by a suitable output coupling 146.

Y Modulation of the input energy may be effected by a control grid 141 interposed between cathode and accelerating grid I 32, the modulating potentials being impressed between grid 141 and cathode 135 from Va source 150 in any suitablel manner, as shown. Modulating may also be effected by superposing the modulating signal upon reflector electrode 131. In this way the principle yof transit-time modulation is applied to an amplifier device, which may be modulated if desired.

It will be understood that the reflector electrode of any of the above-described embodiments of the present invention may be used as the anode of an auxiliary electron discharge device, in the manner shown in Figs. 7 and 8.

It will also be understood that a control grid adjacent the cathode may be added in any of the above-described embodiments of the present invention. Such control grid may be used in a self-oscillating circuit in the manner shown in Fig. 11 for producing Ya fundamental frequency voltage to besupplied to the reflector electrode when serving as a frequency multiplier. Alternatively, such control grid may be used for modulation purposes, by coupling a source of modulating signal thereto in the manner shown in Fig. 15.

Furthermore, in any of the embodiments described, the average transit time in the reflector field may be selected or adjusted in the manner discussed above relative to Figs. l and 6, to produce Va regenerative action in the reflector field, further reducing input requirements.

The devices of Fig. 7 or 8 may be used with circuits differing from those shown in the drawings. For example, instead of the oscillator circuits shown, the same auxiliary electron discharge device may form a conventional type amplifier, supplied with a fundamental frequency voltage impressed on its control or input electrode from any suitable fundamental frequency source. This forms a convenient and useful Way of exciting the reflector electrode with a fundamental frequency signal.

Since many changes couldbe made in the above 15eh constructiomandlmany apparently.widelmdfferc ent mbodimentspi thsfnventonecollld mda withoutdeparung fromthescope thereefri tended;.that-..allmatter containedfrilrzthe aber l description for shown'incthe aCCQIImI-l ingcdrw ings. shall be; interpreted as.-.illu..Strazlvefmld:1101?V infa :limiting sense;-

What is claimed is: l

1.3.I-Iighgfrequency apparatus-comprising means forfproducingan electron .'streami a .pai-r oizlelef'e.: tron-permeable:electrodes a1ong.the.pathz0l Sai. stream. a first :cavity .resonatorsincluding" Said electrodes as portions. of thewalls'ithereof: an' ector, electrode: .in the; .path of Vsaid.fstneam .f .be-:i yond jisaidA electrodes,a .second cavity- .resoundincoupled! between' .said.;.reflector,-..electrode-@and 01165 of;said@ieiectronfpermeable: electrodesfasaid firsts cavityaresonator bein'gtunedgto \a..sfreduencyfsup; stantially. harmonically -..relatedr3to the.;.resell@Dit` frequency of said :second cavityfresonatorg; and meanszfcoupled to saidsecond.resonatorformules;r plyingrenergy :to:v said fsecondycavity. resonator.' 0f.; a frequency .substantially equal; to, said resonarllrl frequency, wherebyf; energy... of. aa, freqllelf harmonically related to .saidlsupplied-:cnergy free; quencyf may :be .extracted z from said ffirstfcavity resonator;

2r Ultra-highf'frequency frequency multiply-L ing iapparatus y comprising means for yproducing.

an electron stream, a pair ofelectronpermeables electrodes; .disposed ein@ the ...path `of;saidi'stlelrrl and lproviding.; axnarrow .gap thereloetween;` faires. flector. .electrode in the.. path: offfsaidestreanrf bef-z yond saidfelectrodes, circuit',meansgconnectedfto saidreflector electrodefor. applying an electron:

retarding potentialzfito said reflector:- electrode, whereby-said electrons .arefreturned through said gap, means. coupled Ato said reflector:.electrodeifqr superposing :onLsaidV retarding-.lpotential aiyoltage;

of: the.l fundamentahfrequency..to.1be...multiplied and a tuned circuit coupled to said electrodes andatunedsubstantially :td-aA harmonicof" said fLLndamental-frequency.-

3. Ultra high. frequency .appara-tus comprisingmeans forv producing .an electronfstreamz al. cavity resonator having a. pair of. electron-permeable Walls along .the path: -.of:said;stream;..a reflector electrode. in said;patl'lzloeyond..saidfelectrodesg-Jandv circuiti means .connected to saidireflectorz elec.-

trode for. impressing a fundamental.:frequencyto r be multiplied. on` said reflector.: electrodegi.- said resonator.. beingtun'ed. to a..harmonic., of. said fundamental ifrequencm.. whereby` energy of .said harmonic frequency may i :be derivedY from Vsaid resonator.

4;. High .frequency apparatus comprisingmeans including a catliodewfor `producing anl-.electron stream, :an annular cavity fresonatorrsurrounding said; cathode, a reflector electrode .in the pathlof said.: stream for. reflecting .electrons- -from Asaid cathode .through said resonator;. and means: cone nected-.to said reflector electrodeorflvarying. the potential of :said .reilector .electrode .atf'a .funda-.-` mental .r.frequency,.. said cavity resonator being tuned Sto. a .harmonic` of frsaidi:fundamentalfreel queney, whereby.I harmonic frequency@v energy'lis supplied .to said. cavity .resonatory Abyesaid stream for. extracting therefrom. l

5. Apparatus as...v in.; claim: 4,'. wherein .said

potential-Varyingmeans .comprises-aufoscillator f circuit. including :said vreflector.electrode asza :por-

tionthereof 6. High; frequency apparatiis=fcomprisinge a cathode, a grid and a reflector electrodemounted in-:alig-nment,;,an. oscillator-circuiti including-said stream-,beyondhthecpoint of interaction of said stream, with saidv reflector electrode.

'7. lFreqilyeric3yr-multiplying apparatus comprise inggmeans V.forV producingY an electron stream,v

meansiincludinga reflector electrode inthe path.y offsaidfstream .forf reversing the direction oftheelectronszvof said stream, circuit means connected tozzsaidreflectorelectrode for varyingV the poten,-l

tial ofisaid reflector .electrode at a fundamental., frequencyfto-.pe multiplied, and means located inv the path ofgsaidelectron stream beyond the pointl of .interaction of said stream with said reflector. electrodefor extractinghigh frequency energy from -said reflected stream at a harmonic of said fundamental frequency.

8;" Frequency-multiplying apparatus compris-Y ing.;j means for producing an electron stream, means `located' in the path f of Vsaid-stream, for providing a retarding electric. eld along the pathr ofzsaid streamyfor retardingand reversing the electronspf said rst-ream, circuit means coupledV to said -first recited` means for Varyingsaid re tarding field at a fundamentalfrequency to be multiplied.; andmeanslocated in the pathof said electronistream beyondthe. point Aof its reversal. forextracting .energy -fromvsaid` reversed .electronl stream ata harmonic. of f said. fundamental `free` quencyg.:

9;;'High' frequency amplifier.. apparatus :coma prising cathode-means. for. vproducing .an electron stiea-m,\.\ ani accelerating .electrode .aligned ywith saiduicathode, said cathodel .means and said.. ac-

rcelerating electrode adaptedto produce a con-.-

stant velocity=..electron:y stream,v a `reflector elec an." input-cavity: resonator .coupled .between said reflector .electrode/and said .accelerating electrode, circuit'fmeans. connected." to said reflector. elec! tro deiforemainta-ining said :reflector electrode at a negative.potential withrespect vto vsaid accelera-Y ating 1 electrodes whereby the electrons` of.: said stream 1 are reversed ini f1ight,. circuit ,meansi cou-.1 pled to said input Icavity f resonator forv exciting said. iniputiresonatorA by..a:.signa1 to. be amplified, whereby-=the potential.. of said. freflector. electrode isr-.periodicallyfvaried. said. signal, :and output cavi-tyiresonatoremeans. tunedsubstantially tothe frequencyf of said. signaleand Alocated -in the 7pathof ..fsaid.;reversed.`v electronJ stream, whereby an ampl-iedrversion of .saidinput signaLmay be dee. rivedlfromesaid outputzresonator.

IOJLHigh frequency apparatus comprising a cathode, ani accelerating...electrode aligned.. with saidfcathode; meanscoupled between said cathode and accelerating electrode;forlprojectingiastream of'.v electrons; mthrough 1;. saidtfelectrode, a .reflector electrodeinthelpath of said strearrhcircuit means coupled to saidtrelecton :electrode.for. varying. the pctentia'l..3of said-.reflectorI electrode Y. at .a1-.prede-v terminedfrequency, whereby saidrstream becomes trans-it-timefmodul ated, and means.. located in .the path ofesaid.streamforextracting high frequency energyirfrom saidmodulated: streami.

1 l ;Apparatusras-imclaim :10,fwhereinfsaidpoe tential-yarying:m'eanszcomprisesacavity resona,

17 Y tor coupled between said accelerating electrode and said reflector electrode, and means coupled to said resonator for exciting said resonator at said predetermined frequency.

12. Apparatus as in claim 10, wherein said energy-extracting means comprises a cavity resonator having an electron-permeable wall in the path of electrons reected by said reflector electrode.

13. Apparatus as in claim 10, further comprising circuit means coupled to said reiiector electrode'for adjusting the average reector potential to a value producing a negative resistance, whereby said reflector potential-varying means requires less power.

ARTHUR E. HARRISON. Y

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PA'I'ENTS Number Name Date Re. 22,506 Hahn June 27, 1944 2,128,232 Dallenbach Aug. 30, 1938 2,128,236 Dallenbach Aug. 30, 1938 2,190,511 Cage Feb. 13, 1940 2,190,515 Hahn Feb. 13, 1940 2,220,556 Thorson Nov. 5, 1940 2,259,690 Hansen Oct. 21, 1941 2,402,983 Brown July 2, 1946 2,511,913 Pierce et a1 Dec. 3, 1946 2,416,303 Parker Feb. 25, 1947 

